Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
QUARTERLY INFORMATION
Revenue	$ 2,258,349	$ 2,158,061	$ 2,089,338	$ 1,903,467	$ 1,931,146	$ 1,840,897	$ 1,788,028	$ 1,736,983	$ 8,409,215	$ 7,297,054	$ 6,758,138
Earnings from Continuing Operations Before Income Taxes	111,338	116,140	98,283	48,100	78,577	94,492	80,854	60,622	373,861	314,545	407,256
Earnings from Continuing Operations	108,645	89,511	43,519	33,932	643,318	59,040	51,395	38,536	275,607	792,289	265,232
Net Earnings	$ 108,784	$ 88,751	$ 42,258	$ 33,505	$ 643,808	$ 58,750	$ 50,868	$ 38,406	$ 273,298	$ 791,832	$ 263,069
Earnings from Continuing Operations per Common Share
Earnings from continuing operations per common share — Basic (in dollars per share)	$ 2.07	$ 1.70	$ 0.83	$ 0.65	$ 12.22	$ 1.12	$ 0.97	$ 0.73	$ 5.24	$ 15.00	$ 4.99
Earnings from continuing operations per common share — Diluted (in dollars per share)	2.06	1.69	0.82	0.64	12.12	1.12	0.97	0.72	5.21	14.90	4.95
Net Earnings per Common Share
Basic (in dollars per share)	2.07	1.69	0.80	0.64	12.23	1.12	0.96	0.72	5.20	15.00	4.95
Diluted (in dollars per share)	$ 2.06	$ 1.68	$ 0.80	$ 0.63	$ 12.13	$ 1.11	$ 0.96	$ 0.72	$ 5.17	$ 14.89	$ 4.91